1 Samuel 17:9-12
V9 And Saul eyed David from that day and forward.
V10 And it came to pass on the morrow, that the evil spirit from God came upon Saul, and he prophesied in the midst of the house: and David played with his hand, as at other times: and there was a javelin in Saul's hand.
V11 And Saul cast the javelin; for he said, I will smite David even to the wall with it. And David avoided out of his presence twice.
V12 And Saul was afraid of David, because the LORD was with him, and was departed from Saul.
Saul was jealous of David because the Lord had departed from Saul but with was David. Also, the Lord was blessing David's service and ministry. While David ministered to Saul with his instrument Saul jealously eyed David. Saul threw his javelin at David in 1 Samuel 17:11 and again in 1 Samuel 19:10. Saul's jealousy of David grew so great that he even threw his javelin at Jonathan his own son because Jonathan was protecting David (1 Samuel 20:33).
Notice the contrast between Saul and David. In Saul's hand was a javelin and in David's hand was a harp. Saul's javelin was used for harm. David harp was used for ministry.
Saul's jealousy made him go mad. There's a lesson to be learned about jealousy. James said in James 3:13-16 "if you have bitter jealousy and rivalry in your hearts, stop boasting and slandering the truth. V15 That kind of wisdom does not come from above. No, it is worldly, self-centered, and demonic. V16 For wherever jealousy and rivalry exist, there is disorder and every kind of evil."
These verses truly characterize King Saul. Saul was so jealous of David that when Doeg told Saul that Ahimelech the priest helped David Saul ordered 85 people killed. Many of whom were priests (1 Samuel 22). Saul's jealousy drove him to madness. While Saul was madly jealous David ministered and did the will of God.
We want ministry not madness.